Methods and apparatus for detecting the entry of formation gas into a well bore

ABSTRACT

As a preferred mode for practicing the invention disclosed herein, a discrete sample of drilling mud from the borehole is periodically trapped within an expansible sampling chamber defined between a pair of telescoping members coupled to a drill string adjacent to the drill bit. By moving the drill string so as to expand the sampling chamber, the pressure of the entrapped sample is reduced to at least the saturation pressure of a gascontaining drilling mud at the borehole ambient temperature. By measuring the force required to expand the sampling chamber, the presence or absence of formation gas in the drilling fluid can be determined; and, if desired, these force measurements may be used to derive quantitative measurements which are representative of the percentage of gas entrained in the discrete sample. In the representative embodiments of the apparatus of the present invention disclosed herein, one or more unique sampling devices are arranged between the upper and lower telescoping members of a typical slip joint which is tandemly connected in the drill string preferably a short distance above the drill bit. Each of these fluid samplers includes telescoping piston and chamber members defining an enclosed sample chamber which is expanded in response to extension of the slip joint members. Valve means are cooperatively arranged with each of the sampling devices for admitting a predetermined volume of drilling mud into the sample chamber each time the slip joint is extended.

United States Patent [191 Tanguy et a1.

[22 Filed: Apr. 10, 1972 [21] Appl.No.:242,320

Related 0.8. Application Data [63] Continuation-impart of Ser. No.105,885, Jan. 12,

1971, abandoned.

[52] US. Cl. 73/153 [51] Int. Cl .L E2lb 47/10 [58] Field of Search73/151, 153, 155, 421.5 R;

[56] References Cited UNITED STATES PATENTS 2,280,075 4/1942 Hayward73/19 2,896,917 7/1959 McGarrahan.... 175/318 X 2,937,007 5/1960 Whittle175/317 X Primary Examiner.lerry W. Myracle Attorney, Agent, orFirm-David L. Moseley; Stewart F. Moore; William R. Sherman [57]ABSTRACT 7 As a preferred mode for practiciii'g the invention dis- June4,1974

closed herein, a discrete sample of drilling mud from the borehole isperiodically trapped within an expansible sampling chamber definedbetween a pair of tele' scoping members coupled to a drill stringadjacent to the drill bit. By moving the drill string so as to expandthe sampling chamber, the pressure of the entrapped sample is reduced toat least the saturation pressure of a gas-containing drilling mud at theborehole ambient temperature. By measuring the force required to expandthe sampling chamber, the presence or absence of formation gas in thedrilling fluid can be determined; and, if desired, these forcemeasurements may be used to derive quantitative measurements which arerepresentative of the percentage of gas entrained in the discretesample. In the representative embodiments of the apparatus of thepresent invention disclosed herein, one or more unique sampling devicesare arranged between the upper and lower telescoping members of atypical slip joint which is tandemly connected in the drill stringpreferably a short distance above the drill bit. Each of these fluidsamplers includes telescoping piston and chamber members defining anenclosed sample chamber which is expanded in response to extension ofthe slip joint members. Valve means are cooperatively arranged with eachof the sampling devices for admitting a predetermined volume of drillingmud into the sample chamber each time the slip joint is extended.

52 Claims, 17 Drawing Figures PATENFEBJUH 4 m4 sgal-ag as' sum 1 nr 6Den/s R. Tanguy Joseph F Kishel INVE N TORS ATTORNEY PAFENYEQM 4 m4SHEET 2 BF 6 Denis R. Tqnguy Joseph F. K/shel IN VEN TORS ATTORNEYPATENIEDJUN 47914 3,813,935

sum a, a? 6 F 76.54 FIG 5B Den/'5 R. Tanguy Joseph F K/she/ I INVENTORSPATWEMM 4 I874 SNEE? S B? 6 A w w a. G. 2 max 4 d m n 2 w 0 m 3 m B 7 mF M M F 2 3 i Tl-IE ENTRY OF FORMATION GAS INTO A WELL BORE Thisapplication is a continuation is a continuationin-part of applicationSer. No. 105,885 filed Jan. 12, 1971, now abandoned.

Those skilled in the art will, of course, appreciate that while drillingan oil or gas well, a drilling fluid or so-called mud is customarilycirculated through the drill string and drill bit and then returned tothe surface by way of the annulus defined between the walls of theborehole and the exterior of the drill string. In addition to coolingthe drill bit and transporting the formation cuttings removed thereby,the mud also functions to maintain pressure control of the various earthformations as they are penetrated by the drill bit. Thus, it iscustomary to selectively condition the drilling mud for maintaining itsspecific gravity or density at a sufficiently high level where thehydrostatic pressure of the column of mud in the borehole annulus willbe sufficient to prevent or regulate the flow of high-pressure connatefluids which may be contained in the formations being penetrated by thedrill bit.

It is, however, not at all uncommon for the drill bit to unexpectedlypenetrate earth formations containing gases at pressures greatlyexceeding the hydrostatic head of the column of drilling mud at thatdepth which willoften result in a so-called blowout. It will beappreciated that unless a blowout is checked, it may well destroy thewell and endanger lives and property at the surface. Thus, to beabundantly safe, it might be considered prudent to always maintain thedensity of the drilling mud at excessively high levels just to preventsuch blowouts from occurring. Those skilled in the art will appreciate,however, that excessive mud densities or so-called mud weightssignificantly impair drilling rates as well as quite often unnecessarilyor irreparably damage potentially-producible earth formations which areuncased. As a matter of expediency, therefore, it is preferred that thedrilling mud be conditioned so as to maintain its density at a levelwhich is just sufficient to at least regulate, if not prevent, theunexpected entry of high-pressure formation fluids into the borehole andinstead rely upon one or more of several typical operating techniquesfor hopefully detecting the presence of such formation fluids in theborehole. I

Many techniques have, of course, been proposed for detecting thepresence of such'high-pressure fluids in the borehole with varyingdegrees of accuracy. For example, detection techniques which may be usedinclude observing changes in'the rotative torque as well as thelongitudinal drag on the drill string, monitoring differencees betweenthe flow rates of the inflowing and outflowing streams of the drillingmud as well as measuring various properties of the returning mud streamand the cuttings being transported to the surface thereby. Those skilledin the art will appreciate, however, that none of the several techniqueswhich are presently employed will reliably and immediately detect theentry of high-pressure gases into the borehole. For example, variationsof torque or drag on the drill string are not always reliableindications since borehole conditions entirely unrelated to the presenceof highpressure gases in the borehole mud can be wholly responsible forcausing significant variations in these parameters. On the other hand,although such techniques as monitoring of the mud flow rates ormeasuring the physical characteristics of the returning mud stream maywell reliably indicate the entrance of high-pressure formation gasesinto the borehole, the interval of time 5 required for a discrete volumeof mud containing such gases to reach the surface may well be in theorder of several hours. This, of course, will usually be too late topermit preventative measures to be taken to avoid a disastrous blowout.

Accordingly, it is an object of the present invention to provide new andimproved methods and apparatus for reliably detecting the entrance ofeven minor amounts of formation gas into a borehole being drilled andthen immediately providing a positive indication at 5 the'surface thatsuch gases are present.

This and other objects of the present invention are attained byentrapping a sample of drilling mud in a variable-volume fluid chamberwhich is cooperatively coupled to the drill string at a selectedlocation above the drill bit and adapted for expansion uponpredetermined movement of the drill string; moving the drill string toexpand the fluid chamber for reducing the pressure of the drilling mudsample to at least the saturation pressure at the ambient boreholetemperature of a gas-containing drilling mud; and measuring the forceapplied to the drill string for expanding the fluid chamber fordetermining a function which is characteristic of the presence orabsence of gas in the drilling mud sample.

To practice the methods of the present invention, the preferredembodiments of the new and improved apparatus described and claimedherein each include a pair of telescoped members which are tandemlycoupled in the drill string for selective movement between exmembers arecooperatively arranged between the telescoping members for defining avariable-volume sample chamber having a minimum volume when thetelescoping drill string members are in one of their positions and amaximum volume whenever the drill string members are moved to theirother position. Valve means are cooperatively arranged for admittingonly a predetermined volume of drilling mud into the sample chamber inresponse to a predetermined movement of the telescoping members so that,upon movement of the telescoping members toward their other position,the volume of the sample chamber will be sufficiently expanded to insurethat the pressure of the entrapped mud sample will be reduced to atleast the saturation pressure of a gas-containing mud sample at ambientborehole temperatures. Means are further provided for measuring theforce applied to the drill string for accomplishing the expansion of thesampling chamber so that determinations may be readily made at thesurface as to whether or not the drilling mud sample is free ofentrained formation gas.

The novel features of the present invention are set forth withparticularity in the appended claims. The invention, together withfurther objects and advantages thereof, may be best understood by way ofthe following description of exemplary methods and apparatus employingthe principles of the invention as illustrated in the accompanyingdrawings, in which:

FIG. 1 schematically illustrates a portion of typical rotary drillingrig and its associated equipment and drill string along with oneembodiment of apparatus arranged in accordance with the presentinvention;

tended and contracted positions. Piston and chamber FIG. 2 is anenlarged cross-sectional view of the embodiment of the present inventionshown in FIG. 1;

FIGS. 3A-3C successively depict various positions of the apparatusillustrated in FIG. 2 during the performance of the methods of thepresent invention;

FIGS. 4A-4D graphically represent certain principles of the presentinvention;

FIG. 5A is a view similar to FIG. 2 but showing an alternativeembodiment of apparatus arranged in accordance with the principles ofthe present invention;

FIG. SB depicts the apparatus of FIG. 5A during the performance of themethods of the present invention;

FIGS. 6A and 6B are successive, enlarged crosssectional views of anotherpreferred embodiment of apparatus of the present invention;

FIGS. 7A and 7B schematically depict successive positions of theapparatus illustrated in FIGS. 6A and 68 during its operation; and

FIGS. 8A-8B graphically represent the operational principles of theapparatus of the present invention depicted in FIGS. 6A and 68.

Turning now to FIG. ll, a new and improved testing tool 10 arranged inaccordance with the present invention is depicted as being tandemlycoupled in a typical drill string 11 comprised of a plurality of jointsof drill pipe 12, one or more drill collars 13, and a rotary drillingbit l4. As is customary, the drilling operation is accomplished by meansof a typical drilling rig 15 which is suitably arranged for drilling aborehole 16 through various earth formations, as at 17, until a desireddepth is reached. To accomplish this, the drilling rig 15 conventionallyincludes a drilling platform 18 carrying a derrick 19 which supportsconventional cable-hoisting machinery (not shown) suitably arranged forsupporting a hook 20 which is coupled thereto by means of aweight-measuring device 21 having an indicator or recorder 22 arrangedtherewith. As is customary, the hoisting hook 20 supports a so-calledswivel 23 and a tubular kelly 24 which is coupled in the drill string 11to the uppermost joint of the drill pipe 12 and is rotatively driven bya rotary table 25 operatively arranged on the rig floor W. The boreholeI6 is filled with a supply of drilling mud 26 for maintaining pressurecontrol of the various earth formations, as at 17; and the drilling mudis continuously circulated between the surface and the bottom of theborehole during the course of the drilling operation for cooling thedrill bit 14 as well as for carrying away earth cuttings as they areremoved by the drill bit. To circulate the drilling mud 26, the drillingrig 15 is provided with a conventional mud-circulating system includingone or more high-pressure circulating pumps (not shown) that are coupledto the kelly 24 and the drill pipe 12 by means of a flexible hose 27connected to the swivel 23. As is typical, the drilling mud 26 isreturned to the surface through the annulus in the borehole 16 aroundthe drill string 11 and discharged via a discharge conduit 28 into aso-called mud pit (not. shown) from which the mud-circulating pumps takesuction.

Turning now to FIG. 2, an enlarged cross-sectional view is depicted ofthe upper portion of the well tool 10. As seen there, the new andimproved testing tool 10 includes an elongated tubular mandrel 29 whichis coaxially arranged in an elongated tubular body 30 and adapted forlongitudinal movement in relation thereto between the contractedposition illustrated and a fullyextended position. To define thelongitudinal positions of the telescoping members relative to oneanother, an

inwardly-opening recess 31 is provided within the axial bore 32 of thebody 30 and adapted for receiving an en- 5 larged-diameter shoulder 33on the mandrel 29. It will be appreciated, therefore, that the extent ofthe longitudinal travel of the telescoping members 29 and 30 isdetermined by the longitudinal spacings between the mandrel shoulder 33and the opposed body shoulders which are respectively defined by theupper and lower surfaces 34 and 35 of the enlarged recess 31. One ormore inwardly-projecting splines 36 are cooperatively arranged on thebody 30 and slidably received within complementary elongated grooves 37formed longitudinally along the exterior of the mandrel 29 forcorotatively securing the telescoping members to one another. In thismanner, the telescoping members 29 and 30 are co-rotatively secured toone another for transmitting the rotation of the drill pipe 12 throughthe testing tool 10 to the drill collars 13 and the drill bit 14therebelow.

To couple the tool 10 into the drill string ll 1, a socket is formed inthe upper end of the mandrel 29 and appropriately threaded, as at 38,for threaded engagement with the lower end of the next adjacent joint ofthe drill pipe 12. Although the lower portion of the tool 38 is notillustrated in FIG. 2, it will be appreciated that the lower end of thebody 30 is either similarly arranged or provided with male threadsadapted for threaded engagement within a complementary threaded socketon the upper end of the next-adjacent drill collar as at 13. In thepreferred embodiment of the well tool 10, a fluid seal 39 is provided onthe enlarged mandrel shoulder 33 for sealing engagement with the innerwall of the recess 31 and one or more wipers 40 are arranged around theupper end of the body 30 to remove accumualtions of mud and the likefrom the spline grooves 37 and the exterior of the mandrel 29.

40 Of particular significance to the present invention,

the new and improved testing tool 10 further includes one or moresimilar or identical fluid-sampling devices, as at 41, which arecooperatively arranged between the telescoping members 29 and 30 forselective operation upon longitudinal movements of the members inrelation to one another. In the preferred embodiment of the testing tool10 shown in FIG. 2, each of the sampling devices 41 includes anelongated body 42 having a longitudinal bore formed in its upper portionand defining a chamber 43 in which an elongated piston 44 istelescopically arranged and adapted for sliding movement relative to thebody between the contracted position illustrated and one or moreextended positions to be subsequently described. Sealing means, such asa upper end of the piston chamber 43, are provided for fluidly sealingthe piston 44 in relation to the body 42. The lower portion of the body42 is cooperatively arranged to provide an enlarged chamber 46 which isseparated from the piston chamber 43 by an inwardlydirected annularshoulder having its lower face suitably shaped, as at 47, for definingan annular valve seat adapted for complementally receiving a valvemember 48 which is movably disposed in the enlarged chamber. Biasingmeans, such as a relatively-weak compression spring 49, arecooperatively arranged in the chamber 46 between the body 42 and thevalve member 48 for suitable O-ring 45 cooperatively arranged near thenormally maintaining the valve member in seating engagement with thevalve seat 47. One or more lateral ports, as at 5%, are arranged in thebody 42 to provide fluid communication between the borehole l6 and theenlarged chamber 46.

For reasons that will subsequently become apparent, the piston member Mis cooperatively arranged to provide an axial bore 51 therein which hasa venting passage 52 at its upper end and receives an elongated rod 53that is slidably disposed therein and extended downwardly therefromthrough a reduced-diameter annular shoulder 54 at the lower end of thebore. Biasing means, such as a moderately-strong spring 55 positioned inthe axial bore 51 between the upper end of the piston member 44 and anenlarged head 56 on the rod 53, are cooperatively arranged for normallyurging the rod downwardly through the valve seat 47 and into engagementwith the opposed face of the valve member 48. Thus, as depicted in FlG.2, so long as the piston 44 remains in its fully-contracted position inrelation to the body 42, the stronger biasing spring 55 will extend therod 53 through the valve seat 4'7 and urge the rod tip against the valvemember 48 for maintaining it out of seating engagement with the valveseat.

In the preferred manner of coupling one or more of the sampling devices41 are to the tool 10, the upper and lower ends of the piston 44 and theelongated body 42 are respectively secured to the telescoping members 29and 30 by means such as hooks 57 and 58 which are releasably coupled totransversely-positioned pins 53 and 60 on the telescoping membersrespectively. Spring-loaded de tents, as at 61, are arranged forretaining the hooks 57 and 58 on their respective pins 59 and 60. Tominimize the overall exterior diameter of the tool Ml, it is preferredto form appropriately-shaped longitudinal recesses, as at 62 and 63, inthe telescoping members 29 and 30 so that once the sampling devices 43releasably secured thereto, they will be substantially or entirelyconfined within the exterior circumference of the tool to reduce thelikelihood that the sampling devices might be damaged as the tool isbeing operated in the borehole l6. 3

Turning now to FIGS. 3A-3C, successive schematic views are shown of thewell tool 10 during the course of a testing operation, withgreatly-enlarged views being shown in each FlG. of one of the fluidsampling devices ll as these elements will appear while a test is beingmade in accordance with the methods of the invention to determinewhether or not gas is then present in the drilling mud 26. As depictedin FIG. 3A, the telescoping members 29 and of the new and improved toollltl are initially fully contracted in relation to one another and thebody 4-2 and the piston 44 of the fluidsampling device All will likewisebe in their fully contracted positions in relation to one another. Solong as the piston member 44 is fully retracted within the body 42, thespring 55 will be effective for urging the rod 53 downwardly against thevalve member 48. Since the spring 55 is somewhat stronger than thespring 49, the net effect will be for the rod 53 to maintain the valvemember 48 spatially disposed below and out of contact with the valveseat 47. Thus, the drilling mud 26 in the borehole 116 immediatelyexterior of the fluidsampling device M will be free to enter the chamber46 by way of the ports to till the lowermost portion of the elongatedbore 43 below the piston 44. It will be recognized, of course, that byvirtue of the venting passage 52, there are no unequal pressure forcesacting on the sampling device at and the piston 44 will remain fullyretracted. The spring will be effective for urging the rod 53 downwardlyto maintain the valve 5 member 48 open against the counteracting closingforce of the spring 49.

It will be appreciated that if the drill string lll is elevated, themandrel 29 will be free to travel upwardly relative to thelongitudinally-stationary body 30 until the shoulder 33 engages theshoulder 34. Conversely, if the drill string lll is maintained at thesame vertical or longitudinal position in relation to the borehole l6while the drill string is being rotated, as the drill bit 14;progressively cuts away the formation materials in 5 contact therewiththe weight of the drill collars 13 will carry the body 30 downwardly inrelation to the longitudinally-stationary mandrel 29 until such timethat the shoulder 33 contacts the shoulder 34. Thus, in either event,the net effect will be to progressively move the telescoped members 29and 30 as well as the body 42 and the piston 44 from their respectiveretracted positions illustrated in H6. 3A toward their respectivemore-extended positions illustrated in FIG. 33.

It will be appreciated, therefore, that upon expansion of the free spacewithin the axial bore 43 as the piston member 44 moves upwardly inrelation to the elongated body 42, the piston member will induct adiscrete volume of the mud 26 into the sampling device 41. As will benoted by comparison of FIGS. 3A and 38, it will be recognized that thevalve member will remain disengaged from the valve seat 47 until suchtime that the inwardly-directed shoulder 54 in the elongated piston 44comes into contact with the enlarged head 56 on the upper end of the rod53. Thus, as shown in H6. 38, once the shoulder 54 engages the enlargedhead 56, the spring 55 is no longer effective for urging the rod 53downwardly so that furtherupward movement of the piston 44 in relationto the body 42 will disengage the tip of the rod from the valve member48 so that the spring 49 will then urge the valve member into seatingengagement with the valve seat 4 7. Once this occurs,

therefore, it will be recognized that a discretevolume of the drillingmud 26 will then be entrapped within the free portion of the axial bore43 as defined at that time between the lower end of the piston 44 andthe valve seat 47. Accordingly, it 'will be recognized that any furtherupward movement of the piston member in relation to the body 42 mustresult in a reduction of the pressure of the entrapped sample of thedrilling mud 26 beforethe tool 10 canassume the position illustrated inFIG. 3C.

To understand the principles of the methods and apparatus of the presentinvention, it must be recognized tron, there would be no significantforces restraining upward travel of the mandrel 29 and the piston 44which is coupled thereto. The pressure of the enthat the physicalcharacteristics of the mud sample env gas to expand accordingly. Thus,in this unlikely situatrapped gas sample would merely be reduced inkeeping with the general gas laws.

As a result, an observer at the surface viewing the weight indicator 22will note a steady increase in the measured reading as upward movementof the drill string llll progressively picks up the weight of the drillpipe 12 and the mandrel 29. Once the shoulder 33 is disengaged from theshoulder 35, the weight indicator 22 will show the entire weight of thekelly 24, the drill pipe 12, and the mandrel 29. This reading will, ofcourse, remain unchanged until the shoulder 33 engages the shoulder 34.From that point on, continued upward movement of the drill string llwill produce a continued increase in the reading shown on the indicator22 until the drill bit M is picked up from the bottom of the boreholelid. The total reading shown on the weight indicator 2.2 will, ofcourse, then be the full weight on the entire drill string lll.

As shown in H6. 4A, the readings, W, of the weight indicator 212 in thisparticular situation when plotted against the upward travel, D, of thedrill string 111 will be generally as graphically represented by thecurve 64. These readings will, therefore, first follow an ascendingsloping line, as at as, until the shoulder 33 is first disengaged fromthe shoulder 35. The indicated weight, W, will then, as indicated at 66,remain constant over that portion of the tool stroke, d,, where theshoulder 33 is moving away from the shoulder 35 and until the valvemember 48 is seated on the valve seat 47 (H6. 3B). As previouslymentioned, even when a gas is trapped in the piston chamber 43 byclosure of the valve member 48, the remaining travel, d of the piston 44will be without significant restraint so that the reading on the weightindicator 22 will remain substantially unchanged (as graphicallyrepresented at 67 in FIG. 4A) until the shoulder 33 engages the shoulder34.

Thereafter, as graphically represented at 68, further upward travel, I),of the drill pipe l2 will again produce an increasing reading, W, on theweight indicator 22 as the weight of the drill collars 13 isprogressively added to that of the drill pipe already supported by thehook 20.

Accordingly, it will be recognized that if only a purely-gaseous sampleis trapped in the piston chamber 43, the readings on the weightindicator 22 will generally be as represented by the curve 64 in FIG.4A. The abrupt changes, as at 69 and 7th, in the slope of the curve 64will clearly define the points during the new and improved testingoperation when the shoulder 33 is respectively disengaging from theshoulder 35 and engaging the shoulder 34. Those skilled in the art willappreciate, therefore, that readings such as those just described willbe readily apparent at the surface since the respective weights of thedrill pipe 12 on the one hand and those of the drill collars l3 and thedrill bit 14 on the other hand are always known with a fair degree ofaccuracy.

This will, of course, induce flashing of the entrapped liquid sample. inthis event, once flashing of the liquid sample commences, the piston 44will then be free to move upwardly toward its extended position untilthe shoulder 33 engages the shoulder 34.

As shown in FIG. 48, therefore, the readings, W, on the indicator 22will generally vary as represented by the graph 7l. where the entrappedsample is initially completely liquid but is ultimately reduced to itssaturation pressure at the ambient borehole temperature. lnitial upwardmovement of the piston 44 toward its intermediate position (FlG. 38)will again cause a steady increase in the reading, W, on the weightindicator 22 until the shouder 33 disengages from the shoulder (thepoint 72 on the curve 71). Then, there will be no further increase inweight (as shown by the line segment 73) until the valve 48 is seated onits associated seat 47 (the point 74 on the curve 7i Further upwardtravel, D, of the drill pipe 12 will then produce a second steadyincrease of observed weight as shown at 75 on the curve 'il.

Once the forces tending to separate the piston 44 and the body 42 aresufficient to reduce the pressure of the entrapped liquid sample to itssaturation pressure at the ambient temperature and flashing of thesample is commenced, as shown at 76 in FIG. 48 there will be nosignificant increase in the reading on the weight indicator 22 until theshoulders 33 and 34 are engaged to begin imposing the combined weight ofthe drill collars l3 and the bit 14 onto the hook 2th This will thencause an increasing reading, W, on the indicator as shown at 77.

The third situation that may occur is where a whollyliquid sample istrapped in the piston chamber 433 but the forces tending to separate thepiston a4 and the body 42 are insufficient to induce flashing of thetrapped liquid sample. It will be appreciated that this can occur where,for a given size of the piston, there is an insufficient number of drillcollars 13 in the drill string lll below the tool 110 to impose asufficient downward force on the tool for allowing the piston 44 to befully extended Thus, the combined weight of the drill collars 13 and thedrill bit ll il is a limiting factor for determining whether acompletely-liquid sample will be flashed during the practice of thepresent inventionAs shown in H6. 4C, therefore, this situation isgraphically represented at '78. It will be recognized that the curve 78is similar to the left-hand portion of the curve 71 in FIG. 4B sofurther explanation is believed unnecessary. It should be noted, ofcourse, that the shoulder 33 will not engage the shoulder 34 so thatextension of the tool It) will be halted just after the valve member 48has closed.

The situation graphically illustrated in H6. 4!) is where a liquid mudsample has only a small percentage of entrained gas. This is, of course,what should usually be expected where a high-pressure gas is initiallyentering the borehole l6 and a blowout is possibly commencing. As shownin FIG. 4D by the curve 79, the initial operation of the tool 10 whileperforming the meth ods of the present invention will be similar to thepreviously-described situations. Once, however, the valve 48 is seated,as at 80 on the curve 79, the continued upward travel of the drill pipe12 will induce movement of the piston 44 toward its fully-extendedposition with substantially less force being required than where theentrapped sample is wholly liquid. This will be readily understood whenit is realized that the presence of entrained gas in an entrapped liquidsample will make the saturation pressure of the mixture correspondinglyhigher than that of a purely lquid sample. Thus, less force is requiredto fully extend the telescoping members 29 and 30 and the body 42 andthe piston 14. This is graphically represented by the curved segment 81of the curve 79.

Accordingly, it will be recognized by considering FIGS. LA-41) that therelationship of the force applied for elevating the drill pipe 12 tofully extend the telescoping members 211 and 30 will be wholly dependentupon the physical state of the sample which is entrapped in the pistonchamber 4.3 upon closure of the valve member 48. Thus, as shown in FIG.4A, if the entrapped sample is purely gas, there will be no significantincrease in the force required to move the telescoping members 29 and 30from their fully-contracted position to their fully-extended position.On the other hand, FIGS. 38 and 4C demonstrate that if the entrappedsample is solely a liquid, once the valve member 48 has been seatedthere will be a significant and readily-recognizable increase in theforce required to move the telescoping members 29 and 30 to theirfullyextended position if such is ever reached. As graphicallyrepresented in FIG. 41), however, the presence of even a smallpercentage of gas which may be entrapped in an otherwise wholly-liquidsample will produce only a slowly-ascending increase of the weightreading, W, on the indicator 22. Accordingly, it will be recognized thatin any of the four above-described situations, observing the readings,W, of the weight indicator 22 in conjunction with the upward travel, D,of the exposed end of the drill pipe 12 will provide areadily-detectable surface indication of the state of the drilling mud26 which is then adjacent to the testing tool of the present invention.

The preceding descriptions have assumed that the testing operations wereconducted by elevating the drill pipe 12 in relation to the drillingplatform 10. It will be appreciated, however, that identical reactionswill be obtained where the drill pipe 12 is maintained at about the samelongitudinal position as the drill string 11 is being rotated. If thisis the situation, it will be recognized that as the drill bit 14continues to cut away at the bottom of the borehole 16, the weight ofthe drill collars 13 and the drill bit will tend to carry the bodies 30and 42 downwardly in relation to the longitudinallystationary mandrel 29and the piston member 44. Thus, the same results as previously describedwill be obtained.

In other words, downward movement of the drill bit 14 will progressivelycarry the body 42 downwardly in relation to thelongitudinally-stationary piston member 44 so that the valve member 48will ultimately be closed once the enlarged rod head 56 engages theshoulder 54. Thereafter, the weight reading, W, which will be registeredby the indicator 22 will again be determined by the nature or state ofthe entrapped fluid within the piston chamber 43. Stated another way,since the combined weight of the drill collars 13 and the drill bit 1 1represent the maximum force which can be effective for moving thetesting tool 10 to its fullyextended position, the above detaileddescriptions are equally applicable regardless of whether it is theupper member 29 and 44 which are being moved upwardly in relation to thelongitudinally-stationary lower members 30 and 42 or it is the lowermembers which are being moved downwardly in relation to thelongitudinallystationary upper members. In either case, easilyrecognized surface indications will be provided to warn the observer ofan impending blowout.

Turning now to FIG. 5A, an enlarged cross-sectional view is shown of theupper portion of another testing tool which is arranged in accordancewith the principles of the present invention. The testing tool 100includes an elongated tubular member 101 which is coaxially disposedwithin an elongated tubular body 102 and suitably arranged forlongitudinal movement in relation thereto between the depicted retractedposition and a fully-extended position. It will, of course, berecognized by comparison of FIGS. 2 and 5A that the testing tool 100 issomewhat similar to the testing tool 10. Thus, for similar reasons, thetelescoping members 101 and 102 are co-rotatively secured to one anotheras by one or more sets of mating splines and grooves as at 103 and 104.Similarly, an enlarged-diameter shoulder 105 on the mandrel 101 iscooperatively arranged within a recess 106 provided within the tool body102 for establishing the contracted and extended positions of thetelescoping members. Other similar details will be noted.

The significant difference between the tool 10 and the tool 100 is,however, that the latter tool has an integral fluid-sampling deviceshown generally at 107 which is cooperatively arranged between thetelescop ing members 101 and 102 for operation in a similar fashion tothe first-described testing tool. In the preferred embodiment of thetesting tool 100 shown in FIG. 5A, the sampling device 107 is providedby arranging a piston chamber 108 in the upper end of the body 102 whichreceives an enlarged-diameter portion 109 of the mandrel 101 having afluid seal 110 operatively disposed therearound. In this manner, uponupward movement of the mandrel 101 in relation to the body 102, the freespace in the piston chamber 108 will be expanded in a similar manner asthe sampling devices 41.

To accomplish the necessary valving action such as previously describedin relation to the sampling devices 41, that portion of the mandrel 101immediately below the enlarged-diameter piston member 109 is reduced indiameter, as at 111, and the next immediately-adjacent portion of themandrel is enlarged in diameter, as at 112, to provide a valve member.In this manner, on the initial upward movement of the mandrel 101, theexpansion of the piston chamber 108 will induce a flow of the drillingmud 26 through one or more lateral ports 113 arranged in the body 102below an inwardly-facing seal 114 which is mounted in the interior bore115 of the body to provide a valve seat for the enlargement 112. Thus,drilling mud will be drawn into the progressively enlarged pistonchamber 108 until the enlargeddiameter portion 112 of the mandrel 101first engages the sealing member 11%. At this point, a discrete sampleof the drilling mud 26 will be entrapped within the piston chamber 108so that further upward travel of the mandrel 101 in relation to the body102 will produce the same variations on the weight indicator 22 as thosepreviously described with reference to FIGS. di t-4D.

From the foregoing descriptions of the new and improved testing tools 10and 100, it will be appreciated from FIGS. 4A-4D that an observer at thesurface can llll readily deduce from the changes in the weight readings,W, on the indicator 22 in association with upward movement of the drillstring ill whether or not gas is then present in the borehole H6 in thevicinity of the drill collars 113. Thus, a simple go-no go" type of testcan be readily performed during the course of the drilling operationmerely by elevating the drill string M a sufficient distance to fullyextend the telescoping members of the testing tool MD (or MP) andobserving the resulting effects as visibly displayed on the weightindicator 22. A test of this nature can, of course, be rapidly conductedwith no appreciable interruption of the drilling operation. Moreover, ifnecessary, several tests can be conducted for verification by simplylowering the drill string if to expel the first sample and repositionthe various elements of the testing tool 10 (or 100).

It should be noted that the new and improved testing tools w and MD arealso capable of performing the methods of the present invention withoutraising the drill string ll ll. Thus, at any time during a drillingoperation, if the drill string ill is slacked off to be certain that thetelescoping members of the testing tool 110 (or 1100) are in theirrespective fully-telescoped positions, as the drilling operationcommences the drill bit 14 will progressively deepen the borehole 116 tomove the telescoping members toward their extended positions. Anobserver can, therefore, note the time interval required for thetelescoped members of the testing tool 10 (or 100) to move to the pointwhere the valve member 48 is first seated (or the enlarged portion 1112is first sealingly engaged with the seal 114). This time interval can,of course, be readily determined at the surface since the pronouncedcessation of the increasing weight indications which occurs once thefull weight of the drill pipe 12 is suspended on the hook will identifywhen the telescoping members first start moving and the next change inthe weight indication will show when the valve member is first seated.

Once it is known how long it takes for the valve member of the testingtool Ml (or lltltl) to be closed, it can be safely assumed that the sametime interval will be required for the telescoping members to move totheir fully-extended positions since the valve closes at the mid-pointof the stroke of the tool. A proportional relationship will, of course,always exist between the times required and d and d irrespective of theactual point in the stroke of the telescoping members that the valvemember is seated. Accordingly, by observing the variations in theindicated weight, W, during this second time interval, an observer canreliably deduce whether gas is then present in the borehole 16 adjacentto the drill collars l3. l-lereagain, if during drilling an indicationis routinely obtained that gas is or may be present, it is quite easy tolower the drill pipe 12 to expel the mud sample then in the testing toolH0 (or 100) and then either continue drilling or else elevate the drillpipe to make a second test for verifying the first test.

point that the fluid sample has been entrapped to the point where thepiston is fullyextended, a unique relationship between this force andthe tool displacement ri is determined by the percentages of gas if anywhich is then entrained in the entrapped sample. As previously describedwith reference to FIGS. 48 and 4C, if the entrapped sample is whollyliquid, the rapid changes in the indicated weight, W, on the indicator22 through the stroke, d of the piston member 44 (or 109) within thepiston chamber 43 (or 108) will provide a positive indication at thesurface that the entrapped sample is wholly free of any entrained gas.Conversely, the force required for moving the piston member 44 (or 109)to its fully-extended position will be directly related to thepercentage of gas which is then entrained in'the entrapped fluid sample.This unique relationship is expressed by the equation:

where,

d longitudinal displacement of the telescoping members required toinduct a sample of mud into i the piston chamber;

d maximum longitudinal displacement of the telescoping members betweenthe point where the valve is closed to the point where the telescopingmembers are fully extended;

P hydrostatic pressure of the drilling mud at the depth at which thesample is being taken;

A cross-sectional area of the piston(s);

W weight indication at the time a sample is being inducted into thepiston chamber; and

W weight indication when the telescoping members are first fullyextended.

it should also be understood that once the sample is trapped in thepiston chamber 43 (or 108), the force being indicated on the weightindicator 22 at any given point during the continued movement of thetelescoping members 29 and 30 (or 101 and 102) will be directly relatedto the amount of entrained gas in the sample. This relationship is bestexpressed by the following equation:

% gas (by volume) (Ad/ 2)[( mnz W)/W] X 100% 1 a a Y qwhere,

Ad longitudinal displacement of the telescoping members between thepoint where the valve is closed to the point where the measurement isbeing made;

(I; maximum longitudinal displacement of the telescoping members betweenthe point where the valve is closed to the point where the telescopingmembers are fully extended;

W weight indication at the time the measurement is being taken less theweight of the drill pipe or drill string above the tool. This latterweight must be corrected to account for the buoyancy of the drill pipeor drill string in the particular drilling mud being used; and

W the product of depth, mud density, and the area of the samplingpiston(s).

Turning now to FIGS. 6A-6B, successive enlarged cross-sectional viewsare depicted of another well tool 200 which also incorporates theprinciples of the present invention. As seen there, the new and improvedtesting tool 200 includes an elongated tubular mandrel 210 which iscoaxially arranged in an elongated tubular body 202 and adapted forlongitudinal movement in relation thereto between the contractedposition illustrated in FIGS. 6A and 613, a first intermediate positionas schematically shown in FIG. 7A, a second intermediate position justabove the first, and a fully-extended position as depicted in FIG. 7B.The body 202 is reduced slightly, as at 203, and provided with one ormore elongated longitudinal grooves cooperatively arranged to slidablyreceive a corresponding number of outwardly-projecting splines 204 onthe mandrel 201 for co-rotatively securing the telescoping members toone another (FIG. 6A). In this manner, when the tool 200 is substitutedfor the tool 10 shown in'FlG. 1, the telescoping members 201 and 202 areco-rotatively secured to one another for transmitting the rotation ofthe drill pipe 12 through the testing tool 200 to the drill collars 13and the drill bit 14 therebelow. Opposed shoulders 205 and 206 at thelower ends of the splines 204 and the reduced body portion 203 definethe upper limit of telescopic movement of the telescoping 201 and 202relative to one another. It will also be appreciated that the opposedshoulders 207 and 208 provided by the upper ends of the mandrel 201 andthe body 202, respectively, will cooperate to define the lower travellimit or fully-contracted position of these two telescoping members.

To couple the tool 200 into the drill string 11, a socket is formed inthe upper end of the mandrel 201 and appropriately threaded, as at 209,for threaded engagement with the lower end of the next adjacent joint ofdrill pipe 12. The lower end of the body 202 is either similarlyarranged or provided with male threads, as at 210, adapted for threadedengagement within a complementary threaded socket on the upper end ofthe next-adjacent drill collar as at 13. In the preferred embodiment ofthe well tool 200, a fluid seal 211 is mounted within the lower end ofthe body 202 for sealing engagement with the lowermost portion of themandrel 201; and one or more wipers 212 are arranged around the upperend of the body to remove accumulations of mud and the like from thesplines 204 and the exterior of the mandrel.

The new and improved testing tool 200 is further arranged to define anexpansible fluid-sampling chamber 213 between the inner and outermembers 201 and 202, with the upper and lower limits of the chamberbeing determined by spaced, internally-reduced portions 214 and 215 inthe axial bore 216 of the body.

I Fluid ports 217 and 218 are arranged in the body 202 above and belowthe seats 214 and 215 respectively to provide fluid communicationbetween the axial bore 216 and the borehole 16 exterior of the tool 200.

The mandrel 201 is cooperatively arranged to include piston means, suchas an enlarged piston member 219 having sealing members such as one ormore chevron shaped seals 220 mounted thereon, adapted for inductingdrilling mud from the borehole 16 into the sampling chamber 213 as themandrel is moved upwardly in relation to the body 202 between itsretracted position shown in FIGS. 6A and 6B and the first intermediateposition schematically depicted in FIG. 7A. The mandrel 201 is alsoarranged to include valve means such as an enlarged valve. member 221spaced below the piston member 219 and carrying sealing members such asone or more downwardly-directed chevron shaped seals 222. As willsubsequently be explained in greater detail, the seals 220 and 222 andthe reduced bore portions 214 and 215 are cooperatively spaced so thatonce the mandrel 201 is in the intermediate position shown in FIG. 7A,the upper and lower seals will be sealingly engaged with the upper andlower reduced portions, respectively, to fluidly seal an entrapped mudsample in the chamber 213.

It will be appreciated from FIG. 7A, that during that part of the travelof the mandrel 201 in relation to the body 202 from the firstintermediate position where the upper seals 220 first sealingly engagethe upper reduced bore portion to the second intermediate position wherethe upper seals are no longer sealingly engaged with this bore portion,the volume of the sample chamher 213 will be increased in proportion tothe difference in diameter of the upper and lower bore portions 214 and215. Stated another way, as the mandrel 201 moves upwardly between theaforementioned intermediate positions, the volume of the sample chamber213 will progressively expand as more of the largerdiameter pistonmember 219 moves out of the sample chamber and is replaced by thesmaller-diameter valve member 221 on the mandrel.

The expansion volume of the sample chamber 213 will, of course, bedetermined by the difference in diameters between the two mandrelportions 219 and 221 (or, stated another way, the difference between theinternal diameters of the reduced bore portions 214 and 215). The totalor maximum-available expansion of the chamber 213 will, therefore, belimited to that which will be obtained as the mandrel 201 moves over theshort distance where the seals 220 and 222 are both respectively engagedwith the upper and lower bore portions 214 and 215. Thus, the samplechamber 213 will be expanded only as the mandrel 201 is moved betweenthe two intermediate positions which occur only so long as both theupper and lower seals 220 and 222 are simultaneously sealingly engagedwith their respective sealing surfaces 214 and 215. As seen in FlGS. 6Aand 6B, the longitudinal spacing between these two intermediatepositions of the inner and outer members 201 and 202 will, in general,be determined by the axial heights of the seals 220 and 222 as well asof the reduced-bore portions 214 and 215.

Once the mandrel 201 is moved further upwardly, however, the chamber 213will be re-opened whenever oneof the two seals 220 or 222 is no longersealingly engaged with its associated sealing surface 214 or 215. Thus,it will be appreciated that in the operation of the new and improvedtool 200, the piston 219 will ultimately be moved upwardly above thesample chamber 213 to release the sample fromthe chamber as the mandrel201 is moved toward the fully-extended position of the tool 200 asdefined by the abutment of the shoulders 205 and 206 and depicted inFIG. 713.

It will be appreciated that if the drill string 11 is elevated, themandrel 201 will be free to travel upwardly relative to thelongitudinally-stationary body 202 until the shoulder 205 engages theshoulder 206. Conversely, if the drill string 11 is maintained at thesame vertical or longitudinal position in relation to the borehole 16while the drill string is being rotated, as the drill bit 14progressively cuts away the formation materials in contact therewith theweight of the drill collars 13 will carry the body 202 downwardly inrelation to the longitudinally-stationary mandrel 201 until such timethat the shoulder 206 contacts the shoulder 205. Thus,

in either event, the net effect will be to progressively move thetelescoped members 201 and 202 as well as the piston 219 and the valvemember 221 from their respective positions illustrated in FIGS. 6A and6B toward their respective positions illustrated in FIGS. 7A and 7B.

To determine whether or not gas is present in the drilling mud, thetelescoping members 201 and 202 of the new and improved tool 200 areinitially fully contracted in relation to one another so that the pistonmember 219 and the valve member 221 will be in their respectivepositions as depicted in FIGS. 6A and 68. So long as the piston member219 and the valve member 221 are in these positions, the drilling mud inthe borehole 16 immediately exterior of the fluid-sampling tool 200 willbe free to enter the sample chamber 213 by way of the ports 217 and 218to fill the enlarged bore 216 above the seal 211.

It will be appreciated, therefore, that upon expansion of the free spacewithin the axial bore 216 as the piston 219 moves upwardly in relationto the body 202, a discrete volume of the drilling mud will be inductedinto the sampling chamber 213. It should be noted that during movementof the mandrel 201 between the fullycontracted position shown in FIGS.6A and 6B and the first intermediate position shown in FIG. 7A, it isnot essential that the seals 220 be engaged with the body 202 since thepiston 219 will readily displace drilling mud from the chamber 213 byway of the ports 217 as fresh drilling mud is drawn into the samplechamber by way of the ports 218. As previously described with referenceto FIG. 7A, the seals 222 on the valve member 221 will remain disengagedfrom the valve seat 215 until such time that the seals 220 on the pistonmember 219 are engaged with the upper seating surface 214. Once thisoccurs, as depicted in FIG. 7A, it will be recognized that a discreteand known volume of the drilling mud will then be entrapped within thesample chamber 213 as defined at that time between the lower part of thepiston member 219 and the upper part of the valve member 221.Accordingly, any further upward movement of the mandrel 201 in relationto the body 202 must first result in an expansion of the sample chamber213 and, therefore, a corresponding reduction of the pressure of theentrapped sample of the drilling mud as the mandrel moves between itsfirst and second intermediate positions.

To understand the principles of the operation of the new and improvedtool 200, it must be recognized that the physical characteristics of themud sample entrapped in the sample chamber 213 will determine thesequence of events upon further upward movement of the mandrel 201beyond the first intermediate position shown in FIG. 7A. First of all,those skilled in the art will appreciate that if only a gas wereentrapped in the sample chamber 213, further upward travel of themandrel 201 from its first intermediate position shown in FIG. 7A towardits second intermediate position would simply cause the entrapped gas toexpand accordingly. Thus, in this unlikely situation, there would be nosignificant forces restraining continued upward travel of the mandrel201. The pressure of the entrapped gas sample would merely be reduced inkeeping with the general gas laws as the mandrel 201 moves between itsfirst and second intermediate positions. The mandrel 201 would, ofcourse, be easily moved to its fullyextended position as shown in FIG.7B.

The situation just described will, of course, be significantly differentwhere seating of the piston member 219 and closure of the valve member221 traps a sample in the sample chamber 213 that is entirely a liquid.If this is the case, continued upward travel of the drill pipe 12 willsimply be incapable of producing further extension of the mandrel 201 inrelation to the body 202 beyond its first intermediate position unlessthe forces tending to fully extend the mandrel and the body aresufficient to reduce the pressure of the entrapped liquid sample in thechamber 213 to its saturation pressure at the existing ambient boreholetemperature. Thus, for reasons which will subsequently be explained. inthe preferred embodiment of the tool 200 the effective cross-sectionalareas of the piston member 219 and the valve member 221 are purposelyestablished to be certain that these forces are more than sufficient tofully extend the mandrel 201 in relation to the body 202.

As a result, in the operation of the tool 200 of the present invention,the presence of even a minor quantity of gas (e.g., something in theorder of 2-3 percent or more) in the drilling mud will be sufficient toenable the mandrel 201 to be moved in relation to the body 202 from itsfully-contracted position to its fullyextended position with a minimumdegree of restraint. On the other hand, the substantial or total absenceof gas in the drilling mud will result in an extreme force beingrequired to move the inner and outer members 201 and 202 from theircontracted position to their extended position.

To demonstrate that the degree of force required to extend thetelescoping members 201 and 202 will be directly related to the gascontent in the drilling mud, it has been found that the followingequation defines these forces:

Force= (P, X A){l (V X %Gas)/[(V X %Gas) AVA} (Eq. 3)

where,

P,, hydrostatic pressure of the drilling mud at the depth at which thesample is being taken;

A effective pressure area restraining movement of the telescopingmembers 201 and 202 to their fully-extended position (cross-sectionalarea of the piston seat 214 less the cross-sectional area of the valveseat 215);

V volume of the sample chamber 213 when the tool 200 is positioned-asshown in FIG. 6A;

%Gas percentage, by volume, of gas in the drilling mud; and

AV, increase in volume of the sample chamber 213 as the tool 200 isextended from the intermediate position shown in FIG. 6A to the nextintermediate position where the sample chamber is re-opened.

Accordingly, it will be seen from Equation 3 that for a givenarrangement of the tool 200 and hydrostatic pressure, when the gascontent in the drilling mud is zero, the force required to move thetelescoping members 201 and 202 so as to re-open the sample chamber 213will be directly related to the hydrostatic pressure, P,,, and theeffective pressure area, A, and, therefore, quite high. On the otherhand, since the volume, V,, of the sample chamber 213 is preferably muchlarger than the expansion volume, AV,,, the bracketed fraction inEquation 3 will approach unity even with only minor percentages of gasin the drilling mud so that such minor amounts of gas will substantiallyreduce the force F. In a preferred arrangement of the new and improvedtool 200, the volume, V,., of the sample chamber 213 was selected to bein the order of IOO-times the expansion volume, AV With typicalhydrostatic pres sures and an area, A, in the order of 3-sq. inches, theforce, F, will be negligible whenever the gas content exceeds about 1-2percent.

Turning now to FIGS. 8A and 8B, the two usual conditions to beexperienced in operation of the tool 200 are graphically depicted.Taking the situation where there is a moderate to extreme percentage ofgas in the drilling mud an observer at the surface viewing the weightindicator 22 will note a steady increase in the measured reading asupward movement of the drill string 11 progressively picks up the weightof the drill pipe 12 and the mandrel 201. Once the shoulder 207 isdisengaged from the shoulder 208, the weight indicator 22 will show theentire weight of the kelly 24, the drill pipe 12, and the mandrel 201.This reading will, of course, remain substantially unchanged until theshoulder 205 engages the shoulder 206. From that point on, continuedupward movement of the drill string 11 will again produce a continuedincrease in the reading shown on the indicator 22 untilthe drill bit 14is picked up from the bottom of the borehole 16. The total reading shownon the weight indicator 22 will, of course, then be the full weight ofthe entire drill string 11.

As shown in FIG. 8A, the readings, W, of the weight indicator 22 in thissituation when plotted against the upward travel, D, of the drill string11 will be generally as graphically represented by the curve 223. Thesereadings will, therefore, first follow an ascending sloping line, as at224, until the shoulder 207 is first disengaged from the shoulder 208.The indicated weight, W, will then, as indicated at 225, remain constantover that portion of the tool stroke, d,, where the shoulder 207 ismoving away from the shoulder 208 and until the piston member 219 issealed within the reduced bore portion 214 and the valve member 221 isseated on' the valve seat 215. As previously mentioned, when a gas istrapped in the sample chamber 213 by closure of the valve member 221,the short travel, d of the mandrel 201 between the two intermediatepositions will be,

without significant restraint so that the reading on the weightindicator 22 will remain substantially unchanged (as graphicallyrepresented at 226 in FIG. 8A) until the sample chamber 213 isre-opened. Thereafter, as shown at 227 continued travel, d of themandrel 201 until it is halted (where the shoulder 205 engages theshoulder 206) will show an abrupt decrease as in the reading on theweight indicator 22. Once the total load on the hook 20 is reducedslightly to the weight of the kelly 24, the drill pipe 12 and themandrel 201, the reading, W, on the weight indicator 22 will againremain constant until the shoulders 205 and 206 are engaged as themandrel moves through its stroke, d between its second intermediateposition and its fullyextended position. As graphically represented at228, upon engagement of the shoulders 205 and 206, further upwardtravel, D, of the drill pipe 12 will again produce an increasingreading, W, on the weight indicator 22 as the weight of the drillcollars 13 is progressively added to that of the drill pipe alreadysupported by the hook 20.

Accordingly, it will be recognized that if a sample of gas-containingmud is trapped in the sample chamber 213, the readings on the weightindicator 22 will generally be as represented by the curve 223 in FIG.8A. The abrupt changes, as at 229, 227 and 230, in the curve 223 willclearly define the respective points during the testing operation whenthe shoulder 207 is disengaging from the shoulder 208., when the samplechamber 213 is re-opened, and when the shoulder 205 is engaging theshoulder 206. Those skilled in the art will appreciate, therefore, thatreadings such as those just described will be readily apparent at thesurface since the respective weights of the drill pipe 12 on the onehand and those of the drill collars 13 and the drill bit 14 on the otherhand are always known with a fair degree of accuracy.

As previously explained by reference to Equation 3, the situation isreversed when there is no gas in the drilling mud. As described, themandrel will halt in its first intermediate position until the forceacting on the telescoping members 201 and 202 is sufficient to expandthe sample chamber 213. This will, of course, induce flashing of theentrapped liquid sample. In this event, once flashing of the liquidsample commences, the mandrel 201 will then be free to move upwardlybeyond its second intermediate position and then toward itsfully-extended position where the shoulder 205 engages the shoulder 206.

As shown in FIG. 88, therefore, the readings, W, on the indicator 22will generally vary as represented by the graph 231 where the entrappedsample is initially completely liquid but is ultimately reduced to itssaturation pressure at theambient borehole temperatures. Initial upwardmovement of the mandrel 201 toward its first intermediate position (FIG.3) will again cause a steady increase in the reading, W, on the weightindicator 22 until the shoulder 207 disengages from the shoulder 208(the point 232 on the curve 231). Then, there will be no furtherincrease in weight (as shown by the line segment 233) until the pistonmember 219 is sealed within the bore 214 and the valve member 221 isseated on its associated seat 215 (the point 234 on the curve 231).Further upward travel, D, of the drill pipe 12 will then immediatelyproduce a second steady increase of observed weight as shown at 235 onthe curve 231.

Once the forces tending to further separate the mandrel 201 and the body202 are sufficient to reduce the pressure of the entrapped liquid sampleto its saturation pressure at the ambient temperature and flashing ofthe sample is commenced, as shown at 236 in FIG. 5, there will be nosignificant increase in the reading on the weight indicator 22 untilthesample chamber 213 is reopened. I-Iereagain, there will then be anabrupt decrease, as at 237, in the reading, W, on the indicator 22 andthen a steady reading, as at 238, until the shoulders 205 and 206 areengaged to begin imposing the combined weight of the drillcollars 13 andthe bit 14 onto thehook 20. This will again cause an increasing reading,W, on the indicator as shown at 239.

It will be noted, however, that when the telescoping members 201 and 202move from their second extended position to their fully-extendedposition, there will be a sudden impact (as represented by the surge inforce shown at 240 in FIG. 88) as the shoulder 205 momentarily strikesthe shoulder 206. It will be recognized that this sudden shock or impactwill be caused by the momentary release of the forces tending to stretchthe drill pipe 12 as the telescoped members 201 and 202 are movedbetween their two intermediate positions. This impact will, of course,produce a sudden shock force similar to that imposed by a typicaldrilling jar. Those skilled in the art will appreciate that such impactsare easily detected at the surface. Accordingly, in the operation of thenew and improved tool 200 for practicing the methods of the presentinvention, the absence of gas in the drilling mud will produce a spacedsuccession of shocks or impacts which will signify there is little or nogas in the drilling mud. On the other hand, should these impacts cease,it will be known that gas has entered the borehole l6 and appropriatemeasures can be taken.

The preceding discriptions have assumed that the testing operations wereconducted by elevating the drill pipe 12 in relation to the drillingplatform 118. it will be appreciated, however, that identical reactionswill be obtained where the drill pipe 112 is maintained at about thesame longitudinal position as the drill string 111 is being rotated. Ifthis is the situation, it will be recognized that as the drill bit 14continues to cut away at the bottom of the borehole 16, the weight ofthe drill collars l3 and the drill bit will tend to carry the body 202downwardly in relation to the longitudinally-stationary mandrel 2011 andthe piston member 219 and the valve member 2211. Thus, the same resultsas previously described will be obtained.

ln other words, downward movement of the drill bit 14 will progressivelycarry the body 202 downwardly in relation to thelongitudinally-stationary piston member 219 and the valve member 221 sothat the sample chamber 2113 will ultimately be closed. Thereafter, theweight readings, W, which will be registered by the indicator 22 willagain be determined by the nature of state of the entrapped fluid withinthe sample chamber 213. Stated another way, since the combined weight ofthe drill collars l3 and the drill bit 14 represent the maximum forcewhich can be effective for moving the testing tool 200 to itsfully-extended position, the above detailed descriptions are equallyapplicable regardless of whether it is the mandrel R which is beingmoved upwardly in relation to the longitudinally-stationary body 202 orit is the body which is being moved downwardly in relation to thelongitudinally-stationary mandrel. In either case, easily-recognizedsurface indications will be provided to warn the observer of animpending blowout.

From the foregoing descriptions of the new and improved testing tool200, it will be appreciated from FIGS. 8A and 88 that an observer at thesurface can readily deduce from the changes in the weight readings, W,on the indicator 22 in association with upward movement of the drillstring ll whether or not gas is then present in the borehole 16 in thevicinity of the drill collars 113. Thus, a simple go-no go type of testcan be readily performed during the course of the drilling operationmerely by elevating the drill string lli a sufficient distance to fullyextend the telescoping members 20K and 202 of the testing tool 200 andobserving the resulting effects as visibly displayed on the weightindicator 22. A test of this nature can, of course, be rapidly conductedwith no appreciable interruption of the drilling operation. Moreover, ifnecessary, several tests can be conducted for verification by simplylowering the drill string 11 to expel the first sample and repositionthe various elements of the testing tool 200.

It should be noted that the new and improved testing tool 200 is alsocapable of performing the abovedescribed test without raising the drillstring 11. Thus, at any time during a drilling operation. if the drillstring 11 is slacked off to be certain that the telescoping members 201and 202 of the testing tool 200 are in their respective fully-telescopedpositions. as the drilling operation commences the drill bit 14 willprogressively deepen the borehole 16 to move the telescoping memberstoward their extended positions. An observer can, therefore, note thetime interval required for the telescoped members 201 and 202 of thetesting tool 200 to move to the point where the piston member 219 andthe valve member 221 is first seated. This time interval can, of course,be readily determined at the surface since the pronounced cessation ofthe increasing weight indications which occurs once the full weight ofthe drill pipe 12 is suspended on the hook 20 will identify when thetelescoping members 201 and 202 first start moving and the next changein the weight indication will show when the piston member 2119 and thevalve member 221 are first seated.

It should be noted that the piston seals 220 are purposely oriented topreferably withstand a pressure differential acting downwardly.Similarly, the valve seals 222 are also oriented to preferably seal bestagainst a pressure differential acting upwardly. Thus, when the samplingchamber 213 is closed and the mandrel 201 is moved upwardly, the chamberwill be expanded to achieve a reduction in the pressure of the entrappedsample without leakage past the seals 220 and 222. Conversely, byorienting the seals 220 and 222 as depicted, downward movement of themandrel 201 will not tend to sealingly engage the seals with the body202. This will, of course, facilitate returning the telescoped members201 and 202 to their fully-retracted position.

Accordingly, it will be appreciated that the present invention hasprovided new and improved methods and apparatus for detecting the entryor presence of gas in a borehole being excavated and signaling this tothe surface. In practicing the methods of the present invention, adiscrete sample of drilling mud from the borehole is periodicallytrapped within an expansible sam pling chamber defined between a pair oftelescoping members coupled to a drill string adjacent to the drill bit.By moving the drill string so as to expand the sampling chamber, thepressure of the entrapped sample is reduced to at least the saturationpressure of a gascontaining drilling mud at the borehole ambienttemperature. By measuring the force required to expand the samplingchamber, the presence or absence of formation gas in the drilling fluidcan be determined; and, if desired, these force measurements may be usedto derive quantitative measurements which are representative of thepercentage of gas entrained in the discrete sample.

in the representative embodiments of the apparatus of the presentinvention disclosed herein, one or more unique sampling devices arearranged between the upper and lower telescoping members of a typicalslip joint which is tandemly connected in the drill string preferably ashort distance above the drill bit. Each of these fluid samplersincludes telescoping piston and chamber members defining an enclosedsample chamber which is expanded in'response to extension of the slipjoint members. Valve means are cooperatively arranged with each of thesampling devices for admitting a predetermined volume of drilling mudinto the sample chambers each time the slip joint is extended.

While only particular embodiments of the present invention and modes ofpracticing the invention have been shown and described, it is apparentthat changes and modifications may be made without departing from thisinvention in its broader aspects; and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

What is claimed is:

1. A method for determing whether formation gas is present in thedrilling mud in a borehole being excavated by a drill bit coupled to adrill string having upper and lower portions operatively arranged formovement relative to one another between spaced positions and comprisingthe steps of:

entrapping a sample of said drilling mud from a selected depth in saidborehole in an expansible sampling chamber coupled between said upperand lower drill string portions and adapted for expansion upon movementof one of said drill string portions relative to the other of said drillstring portions;

moving one of said drill string portions relative to the other of saiddrill string portions to expand said sampling chamber for reducing thepressure of said mud sample to at least the saturation pressure of agas-containing drilling mud at the ambient borehole temperature; and

obtaining an indication representative of thedifference between theforce required to support said upper drill string portion and the forcerequired to expand said sampling chamber for detecting the presence orabsence of formation gas in said mud sample.

2. A method for determining whether formation gas is present in thedrilling mud in a borehole being excavated by a drill bit coupled to adrill string having upper and lower portions operatively arranged formovement relative to one another between spaced positions and comprisingthe steps of:

entrapping a sample of said drilling mud from a selected depth in saidborehole in an expansible sampling chamber coupled between said upperand lower drill string portions and adapted for expansion upon movementof one of said drill string portions relative to the other of said drillstring portions;

moving one of said drill string portions relative to the other of saiddrill string portions to expand said sampling chamber for reducing thepressure of said mud sample to at least the saturation pressure of agas-containing drilling mud at the ambient borehole temperature;v

moving said one drill string portion relative to said other drill stringportion for relieving said mud sample pressure; and I obtaining anindication representative of the differential between the force requiredto expand said sampling chamber and the force required to relieve saidmud sample pressure for detecting the presence or absence of formationgas in said mud sample.

3. A method for determining whether formation gas is present in thedrilling mud in a borehole being excavated by a drill bit coupled to adrill string having upper and lower portions operatively arranged formovement relative to one another between spaced positions and comprisingthe steps of:

entrapping a sample of said drilling mud from a selected depth in saidborehole in an expansible sampling chamber coupled between said upperand lower drill string portions and adapted for expansion upon movementof one of said drill string portions relative to the other of said drillstring portions; moving one of said drill string portions relative tothe other of said drill string portions to expand said sampling chamberfor reducing the pressure of said mud sample to at least the saturationpressure of a gas-containing drilling mud at the ambient boreholetemperature; and measuring the force required to expand said samplingchamber for detecting the presence or absence of formation gas in saidmud sample. 4. The method of claim 3 further including the steps of:'

moving one of said drill string portions relative to the other of saiddrill string portions to contract said sampling chamber for expellingsaid mud sample;

entrapping a second sample of said drilling mud from said selected depthin said sampling chamber;

moving one of said drill string portions relative to the other of saiddrill string portions to re-expand said sampling chamber for reducingthe pressure of said second mud sample to at least said saturationpressure; and

measuring the force required to re-expand said sampling chamber forverifying the force measurement obtained from expansion of said firstmud sample.

5. The method of claim 3 wherein said one drill string portion is saidupper drill string portion and movement thereof is accomplished byelevating said upper drill string portion.

6. Themethod of claim 3 wherein said one drill string portion is saidlower drill string portion and movement thereof is accomplished bycontinuing to excavate said borehole with said drill bit for loweringsaid lower drill string portion in relation to said upper drill stringportron.

7. A method for determining whether formation gas is present in thedrilling mud in a borehole being excavated by a drill bit coupled to adrill string having upper and lower portions telescopically arrangedtogether for longitudinal movement relative to one another betweenspaced positions and comprising the steps of:

entrapping a sample of said drilling mud from a selected depth in saidborehole in an expansible sampling chamber operatively arranged betweensaid drill string portions and adapted for expansion upon longitudinalmovement of one of said drill string portions from a first of saidspaced positions to a second of said spaced positions relative to theother of said drill string portions;

measuring the force required to support said drill string in saidborehole while said drill string portions are in their said firstposition;

moving one of said drill string portions relative to the other of saiddrill string portions and toward the second of said spaced positions toexpand said sampling chamber for reducing the pressure of said mudsample to at least the saturation pressure of a gas-containing drillingmud at the ambient borehole temperature;

measuring the force required to support said drill string in saidborehole while said drill string portions are in their said secondspaced position; and

comparing said force measurements for determining whether formation gasis present in said drilling mud.

8. The method of claim 7 further including the steps moving one of saiddrill string portions relative to the other of said drill stringportions to contract said sampling chamber for expelling said mudsample;

entrapping a second sample of said drilling mud from said selected depthin said sampling chamber;

remeasuring the force required to support said drill string in saidborehole while said drill string portions are again in their said firstposition;

moving one of said drill string portions relative to the other of saiddrill string portions to re-expand said sampling chamber for reducingthe pressure of said second mud sample to at least said saturationpressure;

remeasuring the force required to support said drill string in saidborehole while said drill string portions are in their said secondspaced position; and

comparing said force remeasurements for verifying the determinationobtained by comparison of said force measurements.

9. The method of claim 7 wherein said one drill string portion is saidupper drill string portion and movement thereof is accomplished byelevating said upper drill string portion.

10. The method of claim 7 wherein said one drill string portion is saidlower drill string portion and movement thereof is accomplished bycontinuing to excavate said borehole with said drill bit for loweringsaid lower drill string portion in relation to said upper drill stringportion.

11. A method for determining whether formation gas is present in thedrilling mud in a borehold being excavated by a drill bit coupled to adrill string having upper and lower portions telescopically arrangedtogether for longitudinal movement relative to one another betweenspaced positions and comprising the steps of:

entrapping a sample of said drilling mud from a selected depth in saidborehole in an expansible sampling chamber operatively arranged betweensaid drill string portions and adapted for expansion upon longitudinalmovement of one of said drill string portions from a first of saidspaced positions to a second of said spaced positions relative to theother of said drill string portions;

measuring the force required to support said drill string in saidborehole while said drill string portions are in their said firstposition;

moving one of said drill string portions relative to the other of saiddrill string portions and toward the second of said spaced positions toexpand said sampling chamber for reducing the pressure of said mudsample to at least the saturation pressure of a gas-containing drillingmud at the ambient borehole temperature;

measuring the force required to support said drill string in saidborehole while said drill string portions are in their said secondspaced position; and

determining the percentage of formation gas contained in said drillingmud from the following equation:

% gas (by volume) (Ad/d )[(W,, WNW] X where,

Ad longitudinal displacement of said drill string portiorrsbetweentheirsaid first and second positions: d maximum possible longitudinaldisplacement of said drill string portions;

W the difference between said force measurements; and

W the product of said borehole depth, the density of said drilling mudand the cross-sectional area of said sampling chamber.

12. The method of claim 11 wherein said one drill string portion is saidupper drill string portion and movement thereof is accomplished byelevating said upper drill string portion.

13. The method of claim 11 wherein said one drill string portion is saidlower drill string portion and movement thereof is accomplished bycontinuing to excavate said borehole with said drill bit for loweringsaid lower drill string portion in relation to said upper drill stringportion.

14. A method for determining whether formation gas is present in aborehole being excavated by a drill bit coupled to a drill string havingtelescoped piston and chamber members cooperatively arranged thereon fordefining therebetween an expansible sampling chamber and adapted forlongitudinal movement relative to one another between a contractedposition where said sampling chamber has a reduced volume and anextended position where said sampling chamber has an increased volumeand comprising the steps of:

moving one of said telescoped members relative to the other of saidtelescoped members from said contracted position toward said extendedposition for inducting a discrete volume of drilling mud into saidsampling chamber;

while said telescoped members are between their said positions, closingsaid sampling chamber for entrapping a sample of said drilling mud insaid sampling chamber; measuring the force required to support saiddrill string in said borehole once said mud sample has been entrapped insaid sampling chamber;

moving said one telescoped member relative to said other telescopedmember and further toward said extended position to expand said samplingchamber for reducing the pressure of said mud sample to at least thesaturation pressure of a gascontaining drilling mud at the ambientborehole temperature; I

measuring the force required to support said drill string in saidborehole after said entrapped mud sample has been expanded in saidsampling chamber; and

correlating said force measurements for determining whether formationgas is present in said mud sample.

15. The method of claim 14 wherein said sampling chamber is expanded byelevating said drill string to raise said one telescoped member towardsaid extended position.

16. The method of claim 14 wherein said sampling chamber is expanded bycontinuing to excavate said borehole with said drill bit for loweringsaid one telescoped member toward said extended position.

17. A method for detecting whether formation gas is present in aborehole being excavated by a drill bit coupled to a drill string havingtelescoped piston and chamber members cooperatively arranged thereon fordefining therebetween an expansible sampling chamber and adapted forlongitudinal movement relative to one another between a contractedposition where said sampling chamber has a reduced volume, first andsecond intermediate positions where said sampling chamber has anincreased volume, and an extended position where said piston member isremoved from said sampling chamber and opposite shoulders on saidtelescoped members are co-engaged, and comprising the steps of:

moving one of said telescoped members relative to the other of saidtelescoped members from said contracted position toward said firstintermediate position for indu'cting a discrete volume of drilling mudinto said sampling chamber;

while said telescoped members are in their said first intermediateposition, closing said sampling chamber for entrapping a sample of saiddrilling mud in said sampling chamber;

once said mud sample has been entrapped in said sampling chamber, movingsaid one telescoped member relative to said other telescoped member tosaid second intermediate position to expand said sampling chamber forreducing the pressure of said mud sample to at least the saturationpressure of a gas-containing drilling mud at the ambient boreholetemperature; and,

after said entrapped mud sample has been expanded in said samplingchamber, moving said one telescoped member relative to said othertelescoped member to said extended position to remove said piston memberfrom said sampling chamber and bring said opposed shoulders togetherwith a force representative of the presence or absence of fonnation gasin said mud sample.

18. The method of claim 17 wherein said telescoped members are movedrelative toone another by elevating said drill string to raise said onetelescoped member toward said extended position.

19. The method of claim 17 wherein said telescoped members are movedrelative to one another by continuing to excavate said borehole withsaid drill bit for lowering said one telescoped memberv toward saidextended position.

20. the method of claim 17 wherein the force required to move said onetelescoped member for bringing said opposed shoulders together isexpressed by the equation:

a where.

P,, hydrostatic pressure of said drilling mud in said borehole adjacentto said sampling chamber;

A effective pressure area restraining movement of said one telescopedmember relative to said other telescoped member;

V volume of said sampling chamber when said telescoped members are intheir said first intermediate position;

AV increase in volume of said sampling chamber resulting from expansionthereof; and

%gas percentage, by volume, of formation gas in said mud sample.

21. Apparatus adapted for determining whether formation gas is presentin the drilling mud in a borehold being excavated and comprising:

a drill string having a drill bit dependently coupled thereto andincluding inner and outer telescoped members tandemly connected thereinand cooperatively arranged for movement relative to one another betweenspaced positions;

first means cooperatively arranged between said telescoped members anddefining an expansible fluid chamber adapted to be expanded from aselected volume to progressively-larger volumes in response to movementof said telescoped members from one of their said spaced positionstoward another of their said spaced positions;

second means cooperatively arranged between said telescoped members andadapted for sequentially admitting a sample of drilling mud into saidfluid chamber as said telescoped members are moved away from their saidone position and then entrapping that sample in said fluid chamber assaid telescoped members are moved toward their said other position; and

third means for obtaining an indication representative of the forcerequired for moving said telescoped members further away from their saidone position after a mud sample is entrapped in said fluid chamber.

22. The apparatus of claim 2K wherein said first means include a bodyassociated with one of said telescoped members and having an internalbore with a reduced-diameter portion and an enlarged-diameter portion,and a piston associated with the other of said telescoped members andarranged in said internal bore for defining therein said fluid chamberand movable therein from said reduced-diameter bore portion into saidenlarged -diameter bore portion in response to said movement of saidtelescoped members further away from their said one position.

23. The apparatus of claim 22 wherein said second means include passagemeans cooperatively arranged between said fluid chamber and the exteriorof said body for admitting drilling mud into said fluid chamber, andvalve means cooperatively associated with said passage means and movablebetween a passageopening position when said telescoped members are intheir said one position and a passage-closing position in response tomovement of said telescoped members toward their said other positionbefore said piston is moved out of said reduced-diameter bore portion.

24. The apparatus of claim 23 wherein said third means include first andsecond opposed shoulders respectively associated with said inner andouter telescoped members for engagement with a force related to the loadon said drill string required to move said telescoped members furtheraway from their said one position.

25. The apparatus of claim 21 wherein said first means include a bodyassociated with one of said telescoped members and having an internalbore, and a pis-

1. A method for determing whether formation gas is present in thedrilling mud in a borehole being excavated by a drill bit coupled to adrill string having upper and lower portions operatively arranged formovement relative to one another between spaced positions and comprisingthe steps of: entrapping a sample of said drilling mud from a selecteddepth in said borehole in an expansible sampling chamber coupled betweensaid upper and lower drill string portions and adapted for expansionupon movement of one of said drill string portions relative to the otherof said drill string portions; moving one of said drill string portionsrelative to the other of said drill string portions to expand saidsampling chamber for reducing the pressure of said mud sample to atleast the saturation pressure of a gas-containing drilling mud at theambient borehole temperature; and obtaining an indication representativeof the difference between the force required to support said upper drillstring portion and the force required to expand said sampling chamberfor detecting the presence or absence of formation gas in said mudsample.
 2. A method for determining whether formation gas is present inthe drilling mud in a borehole being excavated by a drill bit coupled toa drill string having upper and lower portions operatively arranged formovement relative to one another between spaced positions and comprisingthe steps of: entrapping a sample of said drilling mud from a selecteddepth in said borehole in an expansible sampling chamber coupled betweensaid upper and lower drill string portions and adapted for expansionupon movement of one of said drill string portions relative to the otherof said drill string portions; moving one of said drill string portionsrelative to the other of said drill string portions to expand saidsampling chamber for reducing the pressure of said mud sample to atleast the saturation pressure of a gas-containing drilling mud at theambient borehole temperature; moving said one drill string portionrelative to said other drill string portion for relieving said mudsample pressure; and obtaining an indication representative of thedifferential between the force required to expand said sampling chamberand the force required to relieve said mud sample pressure for detectingthe presence or absence of formation gas in said mud sample.
 3. A methodfor determining whether formation gas is present in the drilling mud ina borehole being excavated by a drill bit coupled to a drill stringhaving upper and lower portions operatively arranged for movementrelative to one another between spaced positions and comprising thesteps of: entrapping a sample of said drilling mud from a selected depthin said borehole in an expansible sampling chamber coupled between saidupper and lower drill string portions and adapted for expansion uponmovement of one of said drill string portions relative to the other ofsaid drill string portions; moving one of said drill string portionsrelative to the other of said drill string portions to expand saidsampling chamber for reducing the pressure of said mud sample to atleast the saturation pressure of a gas-containinG drilling mud at theambient borehole temperature; and measuring the force required to expandsaid sampling chamber for detecting the presence or absence of formationgas in said mud sample.
 4. The method of claim 3 further including thesteps of: moving one of said drill string portions relative to the otherof said drill string portions to contract said sampling chamber forexpelling said mud sample; entrapping a second sample of said drillingmud from said selected depth in said sampling chamber; moving one ofsaid drill string portions relative to the other of said drill stringportions to re-expand said sampling chamber for reducing the pressure ofsaid second mud sample to at least said saturation pressure; andmeasuring the force required to re-expand said sampling chamber forverifying the force measurement obtained from expansion of said firstmud sample.
 5. The method of claim 3 wherein said one drill stringportion is said upper drill string portion and movement thereof isaccomplished by elevating said upper drill string portion.
 6. The methodof claim 3 wherein said one drill string portion is said lower drillstring portion and movement thereof is accomplished by continuing toexcavate said borehole with said drill bit for lowering said lower drillstring portion in relation to said upper drill string portion.
 7. Amethod for determining whether formation gas is present in the drillingmud in a borehole being excavated by a drill bit coupled to a drillstring having upper and lower portions telescopically arranged togetherfor longitudinal movement relative to one another between spacedpositions and comprising the steps of: entrapping a sample of saiddrilling mud from a selected depth in said borehole in an expansiblesampling chamber operatively arranged between said drill string portionsand adapted for expansion upon longitudinal movement of one of saiddrill string portions from a first of said spaced positions to a secondof said spaced positions relative to the other of said drill stringportions; measuring the force required to support said drill string insaid borehole while said drill string portions are in their said firstposition; moving one of said drill string portions relative to the otherof said drill string portions and toward the second of said spacedpositions to expand said sampling chamber for reducing the pressure ofsaid mud sample to at least the saturation pressure of a gas-containingdrilling mud at the ambient borehole temperature; measuring the forcerequired to support said drill string in said borehole while said drillstring portions are in their said second spaced position; and comparingsaid force measurements for determining whether formation gas is presentin said drilling mud.
 8. The method of claim 7 further including thesteps of: moving one of said drill string portions relative to the otherof said drill string portions to contract said sampling chamber forexpelling said mud sample; entrapping a second sample of said drillingmud from said selected depth in said sampling chamber; remeasuring theforce required to support said drill string in said borehole while saiddrill string portions are again in their said first position; moving oneof said drill string portions relative to the other of said drill stringportions to re-expand said sampling chamber for reducing the pressure ofsaid second mud sample to at least said saturation pressure; remeasuringthe force required to support said drill string in said borehole whilesaid drill string portions are in their said second spaced position; andcomparing said force remeasurements for verifying the determinationobtained by comparison of said force measurements.
 9. The method ofclaim 7 wherein said one drill string portion is said upper drill stringportion and movement thereof is accomplished by elevating said upperdrill string portion.
 10. The method of claim 7 wherEin said one drillstring portion is said lower drill string portion and movement thereofis accomplished by continuing to excavate said borehole with said drillbit for lowering said lower drill string portion in relation to saidupper drill string portion.
 11. A method for determining whetherformation gas is present in the drilling mud in a borehold beingexcavated by a drill bit coupled to a drill string having upper andlower portions telescopically arranged together for longitudinalmovement relative to one another between spaced positions and comprisingthe steps of: entrapping a sample of said drilling mud from a selecteddepth in said borehole in an expansible sampling chamber operativelyarranged between said drill string portions and adapted for expansionupon longitudinal movement of one of said drill string portions from afirst of said spaced positions to a second of said spaced positionsrelative to the other of said drill string portions; measuring the forcerequired to support said drill string in said borehole while said drillstring portions are in their said first position; moving one of saiddrill string portions relative to the other of said drill stringportions and toward the second of said spaced positions to expand saidsampling chamber for reducing the pressure of said mud sample to atleast the saturation pressure of a gas-containing drilling mud at theambient borehole temperature; measuring the force required to supportsaid drill string in said borehole while said drill string portions arein their said second spaced position; and determining the percentage offormation gas contained in said drilling mud from the followingequation: % gas (by volume) ( Delta d/d2)((Wmax - W)/W) X 100% where,Delta d longitudinal displacement of said drill string portions betweentheir said first and second positions; d2 maximum possible longitudinaldisplacement of said drill string portions; W the difference betweensaid force measurements; and Wmax the product of said borehole depth,the density of said drilling mud and the cross-sectional area of saidsampling chamber.
 12. The method of claim 11 wherein said one drillstring portion is said upper drill string portion and movement thereofis accomplished by elevating said upper drill string portion.
 13. Themethod of claim 11 wherein said one drill string portion is said lowerdrill string portion and movement thereof is accomplished by continuingto excavate said borehole with said drill bit for lowering said lowerdrill string portion in relation to said upper drill string portion. 14.A method for determining whether formation gas is present in a boreholebeing excavated by a drill bit coupled to a drill string havingtelescoped piston and chamber members cooperatively arranged thereon fordefining therebetween an expansible sampling chamber and adapted forlongitudinal movement relative to one another between a contractedposition where said sampling chamber has a reduced volume and anextended position where said sampling chamber has an increased volumeand comprising the steps of: moving one of said telescoped membersrelative to the other of said telescoped members from said contractedposition toward said extended position for inducting a discrete volumeof drilling mud into said sampling chamber; while said telescopedmembers are between their said positions, closing said sampling chamberfor entrapping a sample of said drilling mud in said sampling chamber;measuring the force required to support said drill string in saidborehole once said mud sample has been entrapped in said samplingchamber; moving said one telescoped member relative to said othertelescoped member and further toward said extended position to expandsaid sampling chamber for reducing the pressure of said mud sample to atleast the saturation pressuRe of a gas-containing drilling mud at theambient borehole temperature; measuring the force required to supportsaid drill string in said borehole after said entrapped mud sample hasbeen expanded in said sampling chamber; and correlating said forcemeasurements for determining whether formation gas is present in saidmud sample.
 15. The method of claim 14 wherein said sampling chamber isexpanded by elevating said drill string to raise said one telescopedmember toward said extended position.
 16. The method of claim 14 whereinsaid sampling chamber is expanded by continuing to excavate saidborehole with said drill bit for lowering said one telescoped membertoward said extended position.
 17. A method for detecting whetherformation gas is present in a borehole being excavated by a drill bitcoupled to a drill string having telescoped piston and chamber memberscooperatively arranged thereon for defining therebetween an expansiblesampling chamber and adapted for longitudinal movement relative to oneanother between a contracted position where said sampling chamber has areduced volume, first and second intermediate positions where saidsampling chamber has an increased volume, and an extended position wheresaid piston member is removed from said sampling chamber and oppositeshoulders on said telescoped members are co-engaged, and comprising thesteps of: moving one of said telescoped members relative to the other ofsaid telescoped members from said contracted position toward said firstintermediate position for inducting a discrete volume of drilling mudinto said sampling chamber; while said telescoped members are in theirsaid first intermediate position, closing said sampling chamber forentrapping a sample of said drilling mud in said sampling chamber; oncesaid mud sample has been entrapped in said sampling chamber, moving saidone telescoped member relative to said other telescoped member to saidsecond intermediate position to expand said sampling chamber forreducing the pressure of said mud sample to at least the saturationpressure of a gas-containing drilling mud at the ambient boreholetemperature; and, after said entrapped mud sample has been expanded insaid sampling chamber, moving said one telescoped member relative tosaid other telescoped member to said extended position to remove saidpiston member from said sampling chamber and bring said opposedshoulders together with a force representative of the presence orabsence of formation gas in said mud sample.
 18. The method of claim 17wherein said telescoped members are moved relative to one another byelevating said drill string to raise said one telescoped member towardsaid extended position.
 19. The method of claim 17 wherein saidtelescoped members are moved relative to one another by continuing toexcavate said borehole with said drill bit for lowering said onetelescoped member toward said extended position.
 20. the method of claim17 wherein the force required to move said one telescoped member forbringing said opposed shoulders together is expressed by the equation:Force (Ph X A)(1 - (Vs X %gas)/((Vs X %gas) + Delta Vs )) where, Phhydrostatic pressure of said drilling mud in said borehole adjacent tosaid sampling chamber; A effective pressure area restraining movement ofsaid one telescoped member relative to said other telescoped member; Vsvolume of said sampling chamber when said telescoped members are intheir said first intermediate position; Delta Vs increase in volume ofsaid sampling chamber resulting from expansion thereof; and %gaspercentage, by volume, of formation gas in said mud sample. 21.Apparatus adapted for determining whether formation gas is present inthe drilling mud in a borehold being excavated and comprising: a drillstring having a drill bit dependently coupled thereto and includinginner and outer telescoped members tandemly connected therein andcooperatively arranged for movement relative to one another betweenspaced positions; first means cooperatively arranged between saidtelescoped members and defining an expansible fluid chamber adapted tobe expanded from a selected volume to progressively-larger volumes inresponse to movement of said telescoped members from one of their saidspaced positions toward another of their said spaced positions; secondmeans cooperatively arranged between said telescoped members and adaptedfor sequentially admitting a sample of drilling mud into said fluidchamber as said telescoped members are moved away from their said oneposition and then entrapping that sample in said fluid chamber as saidtelescoped members are moved toward their said other position; and thirdmeans for obtaining an indication representative of the force requiredfor moving said telescoped members further away from their said oneposition after a mud sample is entrapped in said fluid chamber.
 22. Theapparatus of claim 21 wherein said first means include a body associatedwith one of said telescoped members and having an internal bore with areduced-diameter portion and an enlarged-diameter portion, and a pistonassociated with the other of said telescoped members and arranged insaid internal bore for defining therein said fluid chamber and movabletherein from said reduced-diameter bore portion into said enlarged-diameter bore portion in response to said movement of said telescopedmembers further away from their said one position.
 23. The apparatus ofclaim 22 wherein said second means include passage means cooperativelyarranged between said fluid chamber and the exterior of said body foradmitting drilling mud into said fluid chamber, and valve meanscooperatively associated with said passage means and movable between apassage-opening position when said telescoped members are in their saidone position and a passage-closing position in response to movement ofsaid telescoped members toward their said other position before saidpiston is moved out of said reduced-diameter bore portion.
 24. Theapparatus of claim 23 wherein said third means include first and secondopposed shoulders respectively associated with said inner and outertelescoped members for engagement with a force related to the load onsaid drill string required to move said telescoped members further awayfrom their said one position.
 25. The apparatus of claim 21 wherein saidfirst means include a body associated with one of said telescopedmembers and having an internal bore, and a piston associated with theother of said telescoped members and movably arranged in said internalbore for defining therein said fluid chamber.
 26. The apparatus of claim25 wherein said second means include passage means cooperativelyarranged between said fluid chamber and the exterior of said body foradmitting drilling mud into said fluid chamber, and valve meanscooperatively associated with said passage means and movable between apassage-opening position when said telescoped members are in their saidone position and a passage-closing position in response to movement ofsaid telescoped members toward their said other position.
 27. Theapparatus of claim 26 wherein said third means include force-responsivemeans at the surface and adapted for measuring varying loads on saiddrill string as said telescoped members are moved between their saidpositions.
 28. The apparatus of claim 21 wherein said first meansinclude sealing means cooperatively mounted on said inner telescopedmembers and operatively associated with said outer telescoped member fordefining said fluid chamber therebetween.
 29. The apparatus of claim 28wherein said second means include passage means defined between saidtelescoped members for admitting drilling mud into said fluid chamber, afluid seal cooperatively arrangeD on one of said telescoped members insaid passage means, and a sealing surface cooperatively arranged on theother of said telescoped members in said passage means and adapted forsealing engagement with said fluid seal to close said passage means uponmovement of said telescoped members toward their said other position.30. The apparatus of claim 29 wherein said third means includeforce-responsive means at the surface and adapted for measuring varyingloads on said drill string as said telescoped members are moved betweentheir said positions.
 31. Apparatus adapted for determining whetherformation gas is present in the drilling mud in a borehole beingexcavated and comprising: a drill string having a drill bit dependentlycoupled thereto and including inner and outer telescoped memberstandemly connected therein and cooperatively arranged for upward anddownward movements relative to one another between longitudinally-spacedpositions; fluid-sampling means including a body operatively associatedwith one of said telescoped members and having an internal bore, apiston operatively associated with the other of said telescoped membersand movably disposed in said internal bore of said body for definingtherebetween an expansible fluid chamber adapted to be expanded from aselected reduced volume when said telescoped members are in arelatively-contracted position to a selected increased volume when saidtelescoped members are in a relatively-extended position, passage meansbetween said fluid chamber and the exterior of said fluid-samplingmeans, and valve means cooperatively arranged with said fluid-samplingmeans and selectively operable in response to relative movements betweensaid body and said piston for admitting drilling mud through saidpassage means as said fluid chamber is expanded from said reduced volumeto a selected intermediate volume and for blocking said passage means assaid fluid chamber is expanded from said intermediate volume toward saidincreased volume for reducing the pressure of a mud sample entrapped insaid fluid chamber; and force-responsive means adapted for providing anindication at the surface of the force required for expanding said fluidchamber beyond its said intermediate volume to indicate whether gas ispresent in a mud sample entrapped in said fluid chamber.
 32. Theapparatus of claim 31 wherein said body and piston are separate members;and further including means coupling said body to said one telescopedmember; and means coupling said piston to said other telescoped member.33. The apparatus of claim 31 wherein said body and piston are separatemembers respectively disposed exterior of said telescoped members; andfurther including means coupling said body to said one telescopedmember; and means coupling said piston to said other telescoped member.34. The apparatus of claim 31 wherein said force-responsive meansinclude a weight indicator coupled to said drill string and operativelyarranged to provide a first weight measurement of said drill string assaid fluid chamber is being expanded from said reduced volume to saidintermediate volume and to provide a second weight measurement of saiddrill string as said fluid chamber is being expanded from saidintermediate volume toward said increased volume.
 35. The apparatus ofclaim 34 further including means at the surface for determining therelative positions of said body and said piston so that the percentageof gas by volume in a mud sample entrapped in said fluid chamber can bedetermined by the equation: % gas (by volume) ( Delta d/d2)((Wmax - W) X100% where, Delta d longitudinal displacement of said telescoped membersbetween their position defining said intermediate volume where saidfirst load measurement is obtained and their position where said secondload measurement is obtained; d2 maximum longitudinal displacement ofsaid telescoped members betweeN their position defining saidintermediate volume and their said relatively-extended position; W thedifference between said first and second weight measurements; and Wmaxproduct of the borehole depth, the density of the drilling mud in theborehole, and the cross-sectional area of said piston.
 36. The apparatusof claim 34 further including means at the surface for determining whensaid fluid chamber is fully expanded so that the percentage of gas byvolume in a mud sample entrapped in said fluid chamber can be determinedby the equation: % gas (by volume) (d11/d2)(((Ph X A)/(W2 - W1)) - 1) X100% where, d1 longitudinal displacement of said telescoped membersbetween their said relatively-contracted position and their positiondefining said intermediate volume; d2 maximum longitudinal displacementof said telescoped members between their position defining saidintermediate volume and their said relatively-extended position; Phhydrostatic pressure of the drilling mud at the borehole depth at whicha mud sample is being taken; A cross-sectional area of said piston; W1weight indication at the time a mud sample is being inducted into saidfluid chamber; and W2 weight indication when said telescoped membersfirst reach their said relatively-extended position.
 37. The apparatusof claim 31 wherein said valve means include a valve seat defined insaid passage means, a valve member movably disposed in said passagemeans and cooperatively arranged for movement into and out of seatingengagement with said valve seat, and actuating means operative uponrelative movements between said body and said piston for moving saidvalve member into seating engagement with said valve seat as said fluidchamber is expanded beyond said intermediate volume.
 38. The apparatusof claim 31 wherein said valve means include a valve seat defined insaid passage means, a valve member movably disposed in said passagemeans and cooperatively arranged for movement into and out of seatingengagement with said valve seat, and actuating means including firstmeans normally biasing said valve member toward seating engagement withsaid valve seat, an actuating member operatively arranged on said pistonfor retaining said valve member out of seating engagement with saidvalve seat until said body and piston are relatively positioned wheresaid fluid chamber is at its said intermediate volume, and second meansnormally biasing said actuating member against said valve member untilsaid body and piston are relatively positioned where said fluid chamberhas a volume equal to or greater than said intermediate volume.
 39. Theapparatus of claim 31 wherein said valve means include a fluid sealcooperatively arranged on one of said telescoped members in said passagemeans and a sealing surface cooperatively arranged on the other of saidtelescoped members in said passage means and adapted for sealingengagement with said fluid seal to close said passage means uponmovement of said telescoped members for expanding said fluid chamberfrom said intermediate volume toward said increased volume. 40.Apparatus adapted for determining whether formation gas is present inthe drilling mud in a borehole being excavated and comprising: a drillstring having a drill bit dependently coupled thereto and includinginner and outer telescoped members tandemly connected therein andcooperatively arranged for upward and downward movements relative to oneanother between longitudinally-spaced positions; fluid-sampling meansincluding means cooperatively arranged between said telescoped membersfor defining therebetween an expansible fluid chamber adapted to beexpanded from a reduced volume when said telescoped members are in acontracted position to an increased volume when said telescoped membersare in an intermediate position and adapted to be opened when saidtelescoped members are in an extended position, passage means betweensaid fluid chamber and the exterior of said fluid-sampling means, andvalve means cooperatively arranged on said telescoped members andresponsive to relative movements therebetween for admitting drilling mudthrough said passage means as said fluid chamber is expanded from saidreduced volume to a selected intermediate volume and for blocking saidpassage means as said fluid chamber is expanded from said intermediatevolume toward said increased volume for reducing the pressure of a mudsample entrapped in said fluid chamber; and means adapted for providingindications at the surface to determine the differential between theforce required to move said telescoped members between their saidcontracted and intermediate positions and the force required to movesaid telescoped members between their said intermediate and extendedpositions to indicate whether gas is present in a mud sample entrappedin said fluid chamber.
 41. The apparatus of claim 40 wherein said meansdefining a fluid chamber include a longitudinal bore in said outertelescoped member having a reduced-diameter portion and anenlarged-diameter portion, and a piston member arranged on said innertelescoped member and disposed within said longitudinal bore formovement in said reduced-diameter bore portion as said telescopedmembers are moved from their said contracted position to their saidintermediate position and for movement in said enlarged-diameter boreportion as said telescoped members are moved from their saidintermediate position to their said extended position.
 42. The apparatusof claim 40 wherein said indication-providing means include first andsecond opposed shoulders respectively arranged between said telescopedmembers and adapted for co-engagement with a force representative of thepresence or absence of formation gas in a mud sample in said fluidchamber upon movement of said telescoped members to their said extendedposition.
 43. The apparatus of claim 40 wherein saidindication-providing means include a weight indicator coupled to saiddrill string and operatively arranged to provide a first weightmeasurement of said drill string as said fluid chamber is being expandedfrom said reduced volume to said intermediate volume and to provide asecond weight measurement of said drill string as said fluid chamber isbeing expanded from said intermediate volume toward said increasedvolume.
 44. Apparatus adapted for determining whether formation gas ispresent in the drilling mud in a borehole being excavated andcomprising: a drill string having a drill bit dependently coupledthereto; fluid-sampling means cooperatively arranged in said drillstring and including a tubular body tandemly connected to one portion ofsaid drill string and having a longitudinal bore including upper andlower enlarged-diameter bore portions separated at their adjacent endsby a reduced-diameter bore portion, passage means providing fluidcommunication between the exterior of said body and at least one of saidenlarged-diameter bore portions, a tubular mandrel tandemly connected toanother portion of said drill string and telescopically arranged in saidbody for longitudinal movement therein between longitudinally-spacedupper and lower positions, piston means cooperatively arranged on saidmandrel for movement between the other end of said one enlarged-diameterbore portion and said adjacent end thereof for inducting a sample ofdrilling mud therein as said telescoped members are moved from one ofsaid upper and lower positions to a first intermediate position wheresaid piston means enter said reduced-diameter portion and becomesealingly engaged therein, and valve means cooperatively arrangedbetween said telescoped members for fluidly sealing said other end ofsaid one enlarged-diameter bore portion as said telescopEd members aremoved between said first intermediate position and a second intermediateposition where said piston means leave said reduced-diameter boreportion and enter the other of said enlarged-diameter bore portions toexpand a sample of drilling mud inducted into said one enlarged-diameterbore portion; and means adapted for providing indications at the surfacerepresentative of the force required to move said telescoped membersbetween said first and second intermediate positions to indicate whethergas is present in a sample of drilling mud inducted into said oneenlarged-diameter bore portion and released into said otherenlarged-diameter bore portion as said telescoped members are moved fromsaid second intermediate position to the other of said upper and lowerpositions.
 45. The apparatus of claim 44 wherein saidindication-providing means include first and second opposed shouldersrespectively arranged on said body and said mandrel and adapted forimpacting with a force representative of the presence or absence offormation gas in a sample of drilling mud inducted into said oneenlarged-diameter bore portion.
 46. The apparatus of claim 44 whereinsaid indication-providing means include a weight indicator coupled tosaid drill string and operatively arranged to provide at least oneweight measurement of said drill string as said telescoped members aremoved between said first and second intermediate positions.
 47. Theapparatus of claim 44 wherein said indication-providing means include aweight indicator coupled to said drill string and operatively arrangedto provide a first weight measurement of said drill string as saidtelescoped members are moved between said first and second intermediatepositions and a second weight measurement of said drill string as saidtelescoped members are moved between said second intermediate positionand said other position.
 48. The apparatus of claim 44 wherein saidvalve means include a valve seat cooperatively arranged in saidlongitudinal bore in said passage means, and a valve membercooperatively arranged on said mandrel for seating engagement with saidvalve seat at least as long as said telescoped members are moved betweensaid first and second intermediate positions.
 49. The apparatus of calim48 wherein the cross-sectional area of said piston means is greater thanthe cross-sectional area of said valve member.
 50. The apparatus ofclaim 44 wherein said passage means also provide fluid communicationbetween said body exterior and said other enlarged-diameter boreportion.
 51. The apparatus of claim 50 wherein said piston means includean enlarged shoulder on said mandrel, and sealing means on said enlargedshoulder cooperatively arranged to be sealingly engaged only with saidreduced-diameter bore portion.
 52. The apparatus of claim 51 whereinsaid sealing means include a plurality of chevron shaped sealscooperatively arranged to sealingly engage said reduced-diameter boreportion only as said telescoped members are being moved from said firstintermediate position to said second intermediate position.